Ultrasonic transducer for parametric array

ABSTRACT

An ultrasonic transducer having a reduced cost of manufacture. The ultrasonic transducer includes a first insulative retaining layer, a second insulative retaining layer, and a vibrator film layer sandwiched between the first and second retaining layers. The first retaining layer includes a first plurality of apertures formed therethrough, and the second retaining layer includes a second plurality of apertures formed therethrough, in which the second apertures are substantially in registration with the first apertures. The ultrasonic transducer further includes a first cover portion having a plurality of spring/backplate assemblies connected thereto, and a second cover portion. The combination of the first retaining layer, the vibrator film layer, and the second retaining layer is sandwiched between the first and second cover portions of the ultrasonic transducer. The laminated construction of the ultrasonic transducer allows the formation of an array of ultrasonic film transducers using a single piece of ultrasonic vibrator film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior U.S. patentapplication Ser. No. 10/902,901 filed Jul. 30, 2004 entitled ULTRASONICTRANSDUCER FOR PARAMETRIC ARRAY. This application claims priority ofU.S. Provisional Patent Application No. 60/328,516 filed Oct. 9, 2001entitled ULTRASONIC TRANSDUCER.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

BACKGROUND OF THE INVENTION

The present invention relates generally to acoustic transducers, andmore specifically to a high performance ultrasonic transducer having areduced cost of manufacture.

Ultrasonic transducers are known that may be employed in parametricspeaker systems for generating sonic or ultrasonic signals in nonlineartransmission media. For example, an array of ultrasonic transducers maybe employed in a parametric speaker system for generating sonic (i.e.,audio) signals in air or water. A conventional parametric audio systemtypically includes a modulator configured to modulate an ultrasoniccarrier signal with at least one audio signal, at least one driveramplifier configured to amplify the modulated carrier signal, and anultrasonic transducer array comprising a plurality of ultrasonictransducers configured to direct the modulated and amplified carriersignal through the air along a selected path of projection. For example,the ultrasonic transducer array may comprise a plurality ofself-contained electrostatic transducers, piezoelectric transducers,electrostrictive transducers, electro-thermo-mechanical film (ETMF)transducers, or polyvinylidene fluoride (PVDF) film transducers. Becauseof the nonlinear transmission characteristics of the air, the projectedultrasonic signal is demodulated as it passes through the air, therebyregenerating the audio signal along at least a portion of the selectedprojection path.

In the conventional parametric audio system, the level of audible soundproduced by the system is generally proportional to the total surfacearea of the ultrasonic transducer array, and the coverage area of thesound generated by the array. However, this can be problematic because atypical ultrasonic transducer, such as the typical piezoelectrictransducer, has a diameter of only about ¼ inch. As a result, it isoften necessary to include hundreds or even one thousand or morepiezoelectric or electrostatic transducers in the ultrasonic transducerarray to achieve an optimal transducer array surface area.

Although the ultrasonic transducer might be made larger to achievehigher levels of audible sound, this can also be problematic. Forexample, an electrostatic transducer typically includes a backplatemember that is supported by a vibrator film. However, as theelectrostatic transducer increases in size, the size of the backplatealso increases, thereby potentially damaging the thin vibrator filmsupporting the larger backplate. Moreover, each of these smalltransducers is individually connected within the ultrasonic transducerarray and typically configured to be stand-alone operable, which cansignificantly increase both the complexity and the cost of manufactureof the parametric audio system.

It would therefore be desirable to have an improved ultrasonictransducer that can be employed in a parametric speaker system. Such anultrasonic transducer would provide a highly reliable and reduced costsolution to implementing an ultrasonic transducer array within theparametric speaker system.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, an ultrasonic transducer isprovided that may be employed to implement a highly reliable ultrasonictransducer array in a parametric speaker system, while reducing the costof manufacture of the overall system. The presently disclosed ultrasonictransducer has a laminated construction that enables the formation ofmultiple ultrasonic transducers in the ultrasonic transducer array usinga single layer of ultrasonic vibrator film, and a single matrixtransducer housing.

In one embodiment, the ultrasonic transducer comprises a firstinsulative retaining layer, a second insulative retaining layer, and avibrator film layer sandwiched between the first and second retaininglayers. The first retaining layer includes a first plurality ofapertures formed therethrough, and the second retaining layer includes asecond plurality of apertures formed therethrough, in which the secondplurality of apertures is substantially in registration with the firstplurality of apertures. The ultrasonic transducer further comprises afirst cover portion, and a second cover portion. The combination of thefirst retaining layer, the vibrator film layer, and the second retaininglayer is sandwiched between the first and second cover portions.

In the presently disclosed embodiment, the side of the vibrator filmlayer facing the first retaining layer is unmetallized, and the oppositeside of the vibrator film layer facing the second retaining layer ismetallized. The ultrasonic transducer further includes a plurality ofelectrically conductive backplates and a plurality of electricallyconductive springs, which are disposed between the first cover and thevibrator film layer in substantially the same plane as the firstretaining layer. Each backplate is substantially in registration with arespective aperture formed through the first retaining layer, and thebackplate has a shape conforming to the shape of the respectiveaperture. Each spring is disposed between a respective backplate and thefirst cover such that the spring is both mechanically and electricallyconnected to the respective backplate and the first cover, which has anelectrically conductive surface. The first cover portion, the spring,the respective backplate, and the combination of the first retaininglayer, the vibrator film layer, and the second retaining layer, areconfigured to cause the spring to urge the backplate against theunmetallized side of the vibrator film layer through the respectiveaperture.

The combination of the electrically conductive first cover, theplurality of springs, and the plurality of backplates forms a firstelectrode, and the metallized side of the vibrator film layer forms asecond electrode. The ultrasonic transducer is configured to allow avoltage to be applied between the first and second electrodes, therebygenerating an electric field between the vibrator film layer and thebackplates that causes the film to be attracted to the backplates. Inthe event the voltage applied between the first and second electrodes isAC, the film vibrates to generate compression waves at sonic orultrasonic frequencies corresponding to the incoming signal waveform.

In the preferred embodiment, the second cover portion includes aprotective mesh layer and an ornamental cover layer, such that theprotective layer is sandwiched between the second retaining layer andthe ornamental layer. Further, the second retaining layer preferably hasa thickness sufficient to create a spacing between the vibrator filmlayer and the protective and ornamental layers that reduces oreffectively eliminates wave attenuation and/or absorption lossesotherwise caused by the protective and ornamental layers, respectively,over a sonic or ultrasonic bandwidth of interest.

By providing an ultrasonic transducer in the above-described laminatedconstruction that includes the single layer of ultrasonic vibrator film,an ultrasonic transducer array suitable for use in a parametric speakersystem can be manufactured at a reduced cost.

Other features, functions, and aspects of the invention will be evidentfrom the Detailed Description of the Invention that follows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The invention will be more fully understood with reference to thefollowing Detailed Description of the Invention in conjunction with thedrawings of which:

FIG. 1 is a perspective exploded view of an ultrasonic transduceraccording to the present invention;

FIG. 2 is a detailed plan view of a portion of the ultrasonic transducerdepicted in FIG. 1;

FIG. 3 is a block diagram of a parametric audio system including theultrasonic transducer of FIG. 1; and

FIG. 4 is a flow diagram illustrating a method of manufacturing theultrasonic transducer of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional Patent Application No. 60/328,516 filed Oct. 9, 2001entitled ULTRASONIC TRANSDUCER is incorporated herein by reference.

A high performance, highly reliable ultrasonic transducer is disclosedthat has a reduced cost of manufacture. The presently disclosedultrasonic transducer has a laminated construction that allows theformation of multiple ultrasonic film transducers using a single layerof ultrasonic vibrator film and a substantially singular mechanicalstructure.

FIG. 1 depicts an illustrative embodiment of an ultrasonic transducer100, in accordance with the present invention. In the illustratedembodiment, the ultrasonic transducer 100 comprises a first coverportion 102, a first insulative retaining layer 104, a vibrator filmlayer 106, a second insulative retaining layer 108, and a second coverportion 110. As shown in FIG. 1, the vibrator film layer 106 issandwiched between the first and second retaining layers 104 and 108.Further, the combination of the first retaining layer 104, the vibratorfilm layer 106, and the second retaining layer 108 is sandwiched betweenthe first and second cover portions 102 and 110.

Specifically, the vibrator film layer 106 includes a first unmetallized(insulating) side 106.1, and an opposite side 106.2 having a metallic orconductive coating. For example, the vibrator film layer 106 may be madeof a thin film (having a thickness ranging from 0.2-100.0 μm, typically8 μm) of polyester, polyimide, polyvinylidene fluoride (PVDF),polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), or anyother suitable polymeric or non-polymeric material; and, the metallic orconductive coating may comprise, e.g., aluminum, gold, or nickel.Further, the second cover portion 110 includes a protective layer 111and an ornamental layer 112. For example, the protective layer 111 maycomprise a cloth made of wire, a perforated sheet made of metal, or alayer made of any other material (preferably electrically conductive)suitable for protecting the vibrator film layer 106 from damage, whileallowing sonic or ultrasonic compression waves to pass therethrough withminimal attenuation. The ornamental layer 112 may comprise a cover madeof cloth, or any other material suitable for adorning the ultrasonictransducer 100. It is understood that the second cover portion 110 isoptional and may be omitted.

Moreover, the first retaining layer 104 includes a first plurality ofapertures 135 such as an aperture 105 formed therethrough, and thesecond retaining layer 108 includes a second plurality of apertures 139such as an aperture 109 formed therethrough. The first plurality ofapertures 135 is substantially in registration with the second pluralityof apertures 139. For example, each of the apertures 135 and 139 may becircular, square, rectangular, hexagonal, or any other suitablegeometric shape, and may have a diameter of about ½ inch to 4 inches.

The ultrasonic transducer 100 further includes a plurality ofelectrically conductive backplates 116 such as a backplate 117, and acorresponding plurality of electrically conductive springs 114 such as aspring 115, which are disposed between the first cover 102 and thevibrator film layer 106 in substantially the same plane as the firstretaining layer 104. In the presently disclosed embodiment, a respectivebackplate, and at least one respective spring, are provided for each ofthe apertures 135 formed in the first retaining layer 104. It isunderstood, however, that a single compound spring may alternatively beemployed to hold the plurality of backplates 116. Each of the pluralityof backplates 116 is relatively lightweight, and has a shapesubstantially conforming to the shape of the apertures 135 and 139.Further, each of the backplates 116 is substantially in registrationwith a respective one of the apertures 135 formed through the firstretaining layer 104. Moreover, each of the plurality of springs 114 isdisposed between a respective backplate and the first cover 102, suchthat the spring 114 is both mechanically and electrically connected tothe respective backplate and the first cover 102. The first coverportion 102, the springs 114, the backplates 116, and the combination ofthe first retaining layer 104, the vibrator film layer 106, and thesecond retaining layer 108, are configured to cause the resilientsprings 114 to urge the backplates 116 against the unmetallized side106.1 of the vibrator film layer 106 through the respective apertures135.

For example, the backplate 117 is disposed in the aperture 105, which issubstantially in registration with the aperture 109. Further, the spring115 is disposed in the aperture 105 between the backplate 117 and thefirst cover portion 102. Accordingly, the first cover portion 102, thespring 115, the backplate 117, and the combination of the firstretaining layer 104, the vibrator film layer 106, and the secondretaining layer 108, are configured to cause the spring 115 to urge thebackplate 117 against the vibrator film layer 106 through the aperture105.

In the preferred embodiment, the vibrator film layer 106 is laminatedbetween the first and second insulative retaining layers 104 and 108.Specifically, the vibrator film layer 106 and the first and secondretaining layers 104 and 108 are united using any suitable mechanicalfasteners, rivets, and/or adhesives to form a rigid laminated structure,thereby prohibiting the film layer 106 from inadvertently shiftingbetween the retaining layers 104 and 108. For example, a suitableadhesive may be employed to laminate the first retaining layer 104 andthe vibrator film layer 106. Further, the second retaining layer 108preferably has a plurality of threaded holes (e.g., a hole 230, see FIG.2) formed therethrough, which are configured to accept respective screws(not shown) extending through corresponding holes (not shown) in thefirst cover 102 (see FIG. 1) and the first retaining layer 104 forsecurely fastening the first retaining layer 104, the vibrator filmlayer 106, and the second retaining layer 108 to the first cover portion102. It is noted that because the screws may extend through one or moreelectrically active layers, the screws are preferably insulatingfasteners such as nylon screws. The backplates 116 may be made ofaluminum, or any other suitable electrically conductive, lightweightmaterial. Further, the sides (not numbered) of the backplates 116 thatare urged against the vibrator film layer 106 by the respective springs114 preferably have pitted, grooved, and/or textured surfaces, which maybe configured to tailor the acoustic characteristics (e.g., thebandwidth) of the ultrasonic transducer. Moreover, the springs 114 maycomprise coil springs (preferably, conical coil springs), leaf springs,or any other suitable type of spring. The springs 114 are configured toapply a substantially constant force against the vibrator film layer 106to keep the film layer 106 pressed against the backplates 116, withoutwrinkling the film. It is believed that this configuration of thesprings 114 would compensate for film creep, which may occur in thevibrator film layer 106 after being subjected to the force applied bythe springs 114 over an extended period of time.

As described above, the springs 114 are electrically connected to theelectrically conductive first cover 102 and the backplates 116. Thecombination of the first cover 102, the springs 114, and the backplates116 therefore forms a first electrode of the ultrasonic transducer 100.In the preferred embodiment, this first electrode is at ground potentialto provide a degree of electromagnetic shielding in the vicinity of thefirst cover portion 102 of the ultrasonic transducer 100. The metallizedside 106.2 of the vibrator film layer 106 forms a second electrode ofthe transducer 100.

Accordingly, the ultrasonic transducer 100 is configured to allow adrive voltage to be applied between the first and second electrodes ofthe transducer to generate an electric field between the vibrator filmlayer 106 and the backplates 116, thereby causing the film 106 to beattracted to the backplates 116. By applying AC voltages between thefirst and second electrodes, the film can be made to vibrate forgenerating one or more sonic or ultrasonic compression waves. Forexample, the transducer drive signal may be applied to the ultrasonictransducer assembly via a connection cable 118.

In the presently disclosed embodiment, the second cover portion 110 isspaced a predetermined distance from the vibrator film layer 106 by thethickness of the second retaining layer 108. By precisely setting thethickness of the second retaining layer 108, sonic or ultrasonicattenuation caused by the protective layer 111 can be reduced oreffectively eliminated over a selected bandwidth of interest. Forexample, the thickness of the second retaining layer 108 may be set toabout one-eighth of an inch to effectively eliminate ultrasonicattenuation over a bandwidth ranging from approximately 45-55 kHz (orpreferably 45-70 kHz). It should be appreciated that the wavelength ofan ultrasonic compression wave at 55 kHz is about ¼ inch, which is equalto about twice the thickness of the second retaining layer 108 in thisillustrative example. It is noted that the optimal thickness of thesecond retaining layer 108 for achieving an absorption minimum may bedetermined experimentally. This is because the optimal layer thicknessmay be dependent upon the acoustical characteristics (e.g., theimpedance) of the protective layer 111 and the ornamental layer 112.Although there are generally many minima for absorption, the firstabsorption minimum is preferred because it keeps the transducer thin,and permits the highest bandwidth of reduced absorption. Accordingly, inthe preferred embodiment, the thickness of the second retaining layer108 is set to place the second cover portion 110 (including theprotective layer 111 and the ornamental layer 112) approximately ½wavelength from the vibrator film layer 106. It is believed that byplacing the second cover 110 a distance of about ½ wavelength from thevibrator film layer 106, a standing wave is generated between thevibrator film layer 106 and the protective layer 111, thereby allowingenergy to be conserved between the layers 106 and 111 and re-radiatedafter a reflection.

As further described above, the ultrasonic transducer 100 includesscrews (not shown) extending from the grounded first cover portion 102to the second retaining layer 108 of the ultrasonic transducer assembly.In the preferred embodiment, the screws are electrically insulating, andare configured to extend through the threaded holes (e.g., the hole 230,see FIG. 2) in the second retaining layer 108 to the protective layer111. Moreover, the protective mesh layer 111 can be connected to groundpotential by a spring disposed in an “empty” aperture (i.e., an aperturewithout film) to provide a degree of electromagnetic shielding in thevicinity of the second cover portion 110 of the ultrasonic transducer100.

As shown in FIG. 2 depicting a detailed view 200 of the ultrasonictransducer 100 (see FIG. 1), a vibrator film layer 206 is trimmed nearthe hole(s) 230 to prevent the electrically active film layer 206 fromobstructing the hole(s) 230 and inadvertently making electrical contactwith the grounded screw(s) (not shown) passing through the hole(s) 230.It is noted that the spacing of about ½ wavelength from the vibratorfilm layer 106 (see FIG. 1) to the second cover 110 generallyconstitutes a practical operating distance between the electricallyactive film layer 106 and the grounded protective layer 111.

In the preferred embodiment, the insulative ornamental layer 112 isapplied directly to the protective layer 111 with no spacingtherebetween. It is believed that by applying the ornamental layer 112directly to the protective layer 111, absorption losses caused by theornamental layer 112 can be reduced or effectively eliminated over theselected bandwidth of interest. For example, the insulative material ofthe ornamental layer 112 may be secured to the ultrasonic transducerassembly by stretching the material around the protective layer 111, thesecond retaining layer 108, the vibrator film layer 106, and the firstretaining layer 104, and by fastening the material along the peripheryof the first retaining layer 104 between the first retaining layer 104and the first cover portion 102 using a suitable adhesive.

FIG. 2 depicts the detailed view 200 of the ultrasonic transducer 100(see FIG. 1). As shown in FIG. 2, the ultrasonic transducer 200comprises a first cover portion 202, a first insulative retaining layer204 including a plurality of apertures such as an aperture 205 formedtherethrough, the vibrator film layer 206, a plurality of backplatessuch as a backplate 217 substantially in registration with the aperture205, and a connection cable 218 including respective positive andnegative wires.

In the preferred embodiment, the connection cable 218 comprises acoaxial cable to minimize electromagnetic radiation. The connectioncable 218 is mounted in a labyrinth channel 228, which is cut into thefirst retaining layer 204 to provide a degree of strain relief for thecable 218. Further, the negative wire (not shown) of the connectioncable 218 is connected to the above-described first electrode of theultrasonic transducer 200, and the positive wire 229 of the connectioncable 218 is connected to the above-described second electrode of theultrasonic transducer 200.

In the presently disclosed embodiment, the negative wire is connected tothe first electrode via a first piece of electrically conductive tape226 (e.g., copper tape), which may be secured to any convenient part ofthe backplate/spring assembly. In the preferred embodiment, the firstpiece of copper tape is tucked between the coils of at least one spring.The positive wire 229 is connected to the second electrode via a secondpiece of copper tape 220 secured to the inside surface of the secondretaining layer 108 (see FIG. 1). It is noted that the positive wire 229passes through a first opening 221 formed in the vibrator film layer 206to connect to the second piece of copper tape 220. Further, the coppertape 220 faces the metallized side 106.2 of the vibrator film layer 206(see FIG. 2) to allow the tape 220 to make good electrical contact withthe film in the final ultrasonic transducer assembly. In the preferredembodiment, the copper tape 220 extends at least half way across thevibrator film layer 206 to deliver power evenly to the film. Further,silver paint, conductive epoxy, or any other suitable electricalcoupling compound is employed between the copper tape 226 and thebackplate, and between the copper tape 220 and the vibrator film layer206, to improve conductivity. For example, the negative and positivewires of the connection cable 218 may be soldered to the first andsecond copper tapes 226 and 220, respectively.

The ultrasonic transducer 200 optionally includes a bias circuit 222 anda coupling circuit 224. For example, a DC bias signal may be“piggybacked” onto the AC transducer drive signal carried by theconnection cable 218. The coupling circuit 224 is configured to receivethe AC drive signal, and to block the DC bias signal from returningthrough the connection cable 218. The bias circuit 222 is configured togenerate a high voltage DC bias signal, which is employed to amplify theultrasonic transducer output and improve linearity.

In the illustrated embodiment, the bias circuit 222 and the couplingcircuit 224 are disposed in second and third openings 223 and 225,respectively, formed in the vibrator film layer 206. Further, the wire(not numbered) connecting the bias circuit 222 and the coupling circuit224 is disposed in a channel formed in the film to interconnect theopenings 223 and 225.

It should be appreciated that the laminated construction of theultrasonic transducer 100 (see FIG. 1) effectively allows the formationof an array of ultrasonic film transducers, each ultrasonic transducercorresponding to a respective one of the backplates 116. It is furtherappreciated that the ultrasonic transducer array is formed using asubstantially singular piece of ultrasonic vibrator film (e.g., thevibrator film layer 106).

FIG. 3 depicts an illustrative embodiment of a parametric audio system301, which includes an ultrasonic transducer array 300 conforming to theabove-described ultrasonic transducer 100 (see FIG. 1). In theillustrated embodiment, the ultrasonic transducer array 300 is driven bya signal generator 302, which includes an ultrasonic carrier signalgenerator 314 and one or more audio signal sources 304.1-304.n. Optionalsignal conditioning circuits 306.1-306.n receive respective audiosignals generated by the audio signal sources 304.1-304.n, and provideconditioned audio signals to a summer 310. It is noted that suchconditioning of the audio signals may alternatively be performed afterthe audio signals are summed by the summer 310. In either case, theconditioning typically comprises a nonlinear inversion necessary toreduce or effectively eliminate distortion in the reproduced audio. Theconditioning may additionally comprise standard audio productionroutines such as equalization (of audio) and compression.

A modulator 312 receives a composite audio signal from the summer 310and an ultrasonic carrier signal from the carrier generator 314, andmodulates the ultrasonic carrier signal with the composite audio signal.The modulator 312 is preferably adjustable in order to vary themodulation index. Amplitude modulation by multiplication with a carrieris preferred, but because the ultimate goal of such modulation is toconvert audio-band signals into ultrasound, any form of modulation thatachieves that result may be employed.

In a preferred embodiment, the modulator 312 provides the modulatedcarrier signal to a matching filter 316, which is configured tocompensate for the generally non-flat frequency response of a driveramplifier 318 and the ultrasonic transducer array 300. The matchingfilter 316 provides the modulated carrier signal to the driver amplifier318, which in turn provides an amplified version of the modulatedcarrier signal to the multiple ultrasonic film transducers of theultrasonic transducer array 300. The driver amplifier 318 may include aplurality of delay circuits 320 that apply relative phase shifts acrossall frequencies of the modulated carrier signal in order to steer,focus, or shape the ultrasonic beam provided at the output of theultrasonic transducer array 300. The ultrasonic beam, which comprisesthe high intensity ultrasonic carrier signal amplitude-modulated withthe composite audio signal, is demodulated on passage through the airdue to the nonlinear propagation characteristics of the propagationmedium to generate audible sound. It is noted that the audible soundgenerated by way of this nonlinear parametric process is approximatelyproportional to the square of the modulation envelope.

Accordingly, to reduce distortion in the audible sound, the signalconditioners 306.1-306.n preferably include nonlinear inversioncircuitry for inverting the distortion that would otherwise result inthe audible signal. For most signals, this inversion approximates takinga square root of the signal, after appropriate offset. Further, toincrease the level of the audible sound, the ultrasonic transducer array300 is preferably configured to maximize the effective surface area ofthe multiple ultrasonic film transducer.

The frequency of the carrier signal generated by the ultrasonic carriersignal generator 314 is preferably on the order of 45 kHz or higher, andmore preferably on the order of 55 kHz or higher. Because the audiosignals generated by the audio signal sources 304.1-304.n typically havea maximum frequency of about 20 kHz, the lowest frequency components ofsubstantial intensity according to the strength of the audio signal inthe modulated ultrasonic carrier signal have a frequency of about 25-35kHz or higher. Such frequencies are typically above the audible range ofhearing of human beings, and therefore generally have reduced impact onthe human auditory system. A parametric audio system conforming to theconfiguration of the above-described system 301 is disclosed inco-pending U.S. patent application Ser. No. 09/758,606 filed Jan. 11,2001 entitled PARAMETRIC AUDIO SYSTEM, which is incorporated herein byreference.

Having described the above illustrative embodiment, other alternativeembodiments or variations may be made. For example, it was describedthat the first electrode comprising the first cover portion 102 of theultrasonic transducer 100 (see FIG. 1) is grounded to provideelectromagnetic shielding, and that the second electrode comprising themetallized side 106.2 of the vibrator film layer 106 is electricallyactive. However, the vibrator film layer may alternatively be grounded,and the first cover portion may be made electrically active. In thisalternative embodiment, the vibrator film layer poses minimal shockhazard, and therefore the protective mesh layer may generally be placedas close to the film as desired (or the protective layer may be omittedaltogether). It is noted that a shielding layer (not shown) may be addednear the electrically active first cover portion to minimize externallyradiated electromagnetic fields.

It was further described that the parametric audio system 301 (see FIG.3) may include the delay circuits 320 configured to apply relative phaseshifts to the modulated carrier signal to steer, focus, or shape theultrasonic beam generated by the ultrasonic transducer. However, such aphased or “shaded” ultrasonic transducer array configuration mayalternatively be achieved by suitably attenuating or filtering multipledrive signals or individual array elements, and then sending theattenuated/filtered signals to selected regions of the array. Forexample, the vibrator film layer may be grounded, and the multipleattenuated/filtered drive signals may be sent to the selected regions ofthe ultrasonic transducer array via the springs and backplates. Further,a circuit board (not shown) having traces suitable for carrying themultiple drive signals, and for contacting the springs, may be employedin place of the first cover portion of the ultrasonic transducer. Such acircuit board may also include processing circuitry, routing circuitry,and/or other circuitry required to produce the multiple signals drivingthe phased transducer array.

It was also described that the vibrator film layer 106 (see FIG. 1) maybe made of polyester, polyimide, PVDF, PET, PTFE, or any other suitablepolymeric or non-polymeric material. However, in the preferredembodiment, the vibrator film layer is made of a suitable material thatis resistive, so that the film heats up slightly (e.g., by a few degreesCelsius) during operation of the ultrasonic transducer. This slightheating of the vibrator film layer reduces the effects of condensationon the film. By raising the temperature of the vibrator film layer abovethe ambient temperature by resistive heating, the dew point is raised,thereby preventing the formation of condensation on the film andallowing reliable transducer output, even in adverse environmentalconditions.

It is noted that suitable threaded inserts (not shown) may be used tomount the ultrasonic transducer 100 (see FIG. 1) to an externalapparatus. For example, ¼-20 type threaded inserts may be employed tomaintain compatibility with common camera mounting equipment (withappropriate metric adjustments for European use). In the event athreaded insert(s) is located near the center of the ultrasonictransducer, electrically active material (such as the vibrator filmlayer) is generally removed in the proximity of the insert(s) to avoid ashort circuit, and to prevent user exposure to high voltages.

A method of manufacturing an ultrasonic transducer according to thepresent invention is illustrated by reference to FIG. 4. As depicted instep 402, copper tape is secured to the inside surface of the secondinsulative retaining layer for connecting the positive wire to thesecond electrode, and the protective layer is attached to the outsidesurface of the second insulative retaining layer. Next, the vibratorfilm layer is laminated, as depicted in step 404, in between the firstand second insulative retaining layers. The backplates are then dropped,as depicted in step 406, into the respective apertures formed in thefirst retaining layer. Next, the springs are dropped, as depicted instep 408, onto the respective backplates. The positive/negative wiresand bias/coupling circuitry is then added, as depicted in step 410.Next, the ornamental layer is stretched and secured, as depicted in step412, substantially around the protective layer and the first and secondretaining layers. The first cover portion is then secured in place, asdepicted in step 414, to compress the springs, thereby forming the finalultrasonic transducer assembly.

It will further be appreciated by those of ordinary skill in the artthat modifications to and variations of the above-described ultrasonictransducer for parametric array may be made without departing from theinventive concepts disclosed herein. Accordingly, the invention shouldnot be viewed as limited except as by the scope and spirit of theappended claims.

1. An ultrasonic transducer, comprising: a vibrator surface operative togenerate one or more ultrasonic compression waves; a protective coverdisposed on one side of the vibrator surface to allow the ultrasoniccompression waves to pass therethrough, wherein the protective cover andthe vibrator surface are spaced apart a predetermined distancesufficient to minimize absorption and transmission losses due to theprotective cover; and a spacer disposed between the vibrator surface andthe protective cover, wherein the predetermined distance corresponds toa thickness of the spacer.
 2. The transducer of claim 1 wherein thepredetermined distance is about ½ of the wavelength of an ultrasonicwave generated by the ultrasonic transducer.
 3. The transducer of claim1 further including an ornamental layer attached substantially aroundthe protective cover and the vibrator surface.
 4. The transducer ofclaim 3 wherein the ornamental layer is applied directly to theprotective cover with no spacing therebetween.
 5. The transducer ofclaim 3 wherein the ornamental layer comprises a fabric cover.
 6. Thetransducer of claim 1 wherein the protective cover is connected toground potential.
 7. A parametric loudspeaker, comprising: at least oneaudio signal source configured to provide at least one audio signal; amodulator configured to receive a first signal representative of theaudio signal and to convert the first signal into ultrasonicfrequencies; an ultrasonic transducer having a vibrator surfaceoperative to generate one or more ultrasonic compression waves, and aprotective cover disposed on one side of the vibrator surface to allowthe ultrasonic compression waves to pass therethrough, wherein theprotective cover and the vibrator surface are spaced apart apredetermined distance sufficient to minimize absorption andtransmission losses due to the protective cover; and a spacer disposedbetween the vibrator surface and the protective cover, wherein thepredetermined distance corresponds to a thickness of the spacer.
 8. Theparametric loudspeaker of claim 7 wherein the predetermined distance isabout ½ of the wavelength of an ultrasonic wave generated by theultrasonic transducer.
 9. The parametric loudspeaker of claim 7 furtherincluding an ornamental layer attached substantially around theprotective cover and the vibrator surface.
 10. The parametricloudspeaker of claim 9 wherein the ornamental layer comprises a fabriccover.
 11. The parametric loudspeaker of claim 9 wherein the ornamentallayer is applied directly to the protective cover with no spacingtherebetween.
 12. The parametric loudspeaker of claim 7 wherein theprotective cover is connected to ground potential.